1. Field of the Invention
The present invention relates to a protection circuit, and more particularly to an electrostatic discharge protection circuit.
2. Description of the Related Art
With the rapid development of the semiconductor manufacturing technology, the sizes of the elements of the integrated circuits have been reduced to the sub-micron grade for improving the properties and the operation speeds of the integrated circuits. With the reduction of the sizes of the elements, some problems of the reliability thereof appear. More particularly, it will greatly influence the protection capability for the electrostatic discharge (ESD) or the lightning surge of the integrated circuits. In other words, it will greatly reduce the tolerance for the ESD of the elements.
FIG. 1 shows a conventional ESD protection device. Referring to FIG. 1, the single ESD protection device 10 is coupled between an I/O port 11 and a chipset 12. When the I/O port 11 is suffered from a surge voltage, it will generate an excessive current which is called a surge current. At this moment, for protecting the chipset 12 from being damaged by the surge current, the protection device 10 will discharge some charge. That is, a part of the current I10 is guided to a ground terminal GND by a protection current 12. A residual current I2 enters the chipset 12. However, the charge of the residual current I11 will still cause the chipset 12 to suffer the electrical overstress (EOS), such that the elements of the chipset 12 are apt to be damaged and the whole system cannot operate normally.
FIG. 2 shows another conventional ESD protection device. That of FIG. 2 is similar with that of FIG. 1, except that of FIG. 2 includes two ESD protection devices. Referring to FIG. 2, the two ESD protection devices 20a and 20b are coupled between an I/O port 21 and a chipset 22. Similarly, when the I/O port 21 is suffered from the surge voltage, the protection device 20b will discharge some charge. Thus a π-type circuit is formed, but it may not achieve a clamping voltage of the protection device 20b. In addition, although the protection devices 20a and 20b will guide parts of the currents I20a and I20b to the ground terminal GND. The charge of the residual current I21 will damage the elements of the chipset 22, and the whole system cannot operate normally.
Therefore, it needs to provide a protection circuit, which can perform the ESD operation and can further reduce the residual current in the chipset after performing the ESD operation.